Carburetor



Jet. 15, 1934a F `E. ASELTINE CARBURETOR 5 sheets-sheet 1 Filed May 1l, 1929 Oct.; 16, i934. F. E. ASELTINE www12 CARBURETOR Filed May ll. 1929 3 Sheets-Sheet 2 3o al az .sa

a4 35 se Patented @et lr6, i934 unirse ilil CCARBUIRER Fred iE. Aseltine, Dayton, @bien assigner, by menne assignments, to Generai Meters Corporation, J Detroit, Mich., a corporation of Deiaware Application May lill, i929, Seriell No.. 362,19@

i9 crains. (ci. asin-es) The present invention relates to carburetors and more particularly to a modied form of plain tube carburetor, that is, to that type of carburetor in which substantially all of the air is supplied through one main air passage and in which no auxiliary air inlet is provided. l

It is the principal object of the present invention to provide a carburetor of that type re= ferred to with novel means tovcontrol the supply 10 of air thereto under all operating conditions, and in which improved means for supplying fuel thereto is provided which is effective to deliver the desired amourt of fuel to the mixing chamber under all operating conditions.

It is a further object of the invention to provide a carburetor of the above mentioned type, which is simple in design, is composed of a vminimum number of parts, and which may be easily and cheaply manufactured. f

With these general objects in' view, one feature of the invention consists in the provision of an air valve to control the passage of air through the main mixing chamber at all engine'speeds, instead of an air passage of xed area, such as An additional feature of the invention comprises a throttle operated pump for supplying additional fuel to the mixing chamber on opening movements of the throttle for the purpose of period and a liquid dash pot for controlling the motion of the aforementioned air valve, which is ladapted to be lled with fuel whenever thel `throttle operated pump is operated.

A still further feature of the inventionjconsists in the provision of a primary mixing or emulsifying chamber, which is supplied with fuel by a nozzle having a plurality of fuel feeding orifices therein, which are rendered successivel'yeiective t0 and which is adapted to supply a primary mixture or an emulsion of fuel and air to the main mixing chamber at a point anterior to the throttle when the throttle is opened, or to a point in the intake passage posterior to the throttle when the throttle 915 is closed. Y

A still further feature of the invention resides in the provision of a main mixing chamber in the form of a Venturi tube, which is adapted tobe inserted in the main lintake passage and has '50 grooves in the exterior surface thereof supplied with fuel emulsion from the primary mixing chamber and which are adapted to communicate respectively with the main mixture passage at 55.' points above and below the throttle to supply fuel is ordinarily employed in a plain tube carburetor.l

enriching the mixture during the acceleration.

mixture whenthe throttle .is either in its open or closed position. e A furtherfeature of the invention consists of novel means for preventing the'aiccumulation of liquid fuel in the main air chamber during operation of the engine.A 1 l Arstill further feature oi the invention consists in an'economizing device comprising a passage' for admitting air to the emulsifying conduit, which is controlled by a valve operable from the V thrttleto regulate the admission of lair thereto and by an additional automatic valve.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accom- 'panying drawings wherein a preferred embodiment of one form of the present invention is clearly shown. Y

In the drawings:

Fig. 1 is a plan view and Fig. 2 a. side elevation t5VI of a carburetor constructed according to the present invention.

Fig. 3 is a section on the line 3 3 of Fig. 2.

Fig. 4 is a section on the line 4 4 of Fig. l.

Fig. 5 is a vfragmentary side elevation viewed 80 from the opposite side of Fig. 2.

Fig. 6 is a fragmentary section on the line 6--6 of Fig. t. l

Fig. '7 is a fragmentary, detail section of the economizing device, which is shown in elevation in Fig. 5.

The carburetor comprising the present invenf tion consists primarily of two main castings indicated by the reference characters A and B, secured together by screws C, the casting A con-. taining the fuel bowl 1 and the main air chamber 2, the admission of air to which is controlled by a. valve'3, hereinafter more fully described. The casting B consists of the cover for the oat chamber i, and has formed therein-the primary o5 mixing Aor el:nulsii'ying chamber d, which'coms municates by means of passages hereinafter described, with a main mixing chamber 5, formed within a Venturi tube 6, positioned in an outlet passage 7, which is adapted to communicate with the main air chamber 2, and is provided with a ange 8 by means of which the carburetor may be be secured to the intake manifold in the conventional manner. The now of fuel mixture through the main mixing chamber iscontrolled by a butterfly throttle 9 of ordinary construction.

Fuel'is supplied from a. main supply tank, not shown, through a fuel `line which is adapted to connect with passage 10, formed in a boss 11 on the casting B.` The inner end of the passage l0 110 communicates with a vertical passage 12 in which a nipple 13, having a restriction 14, is screwed. The restriction 14 constitutes a seat for a fuel valve 15 of square cross section so as tovpermit fuel to flow past the valve when the latter is unseated, and the valve is lcontrolled by a float 16, secured to an arm 17, pivoted on a pin 18, supported by a bracket 19, depending from the casting B and operates to maintain a constant level i of fuel in the chamber 1 'in the conventional manner. A drain plug 20 is screwed into the bottom of the fioat chamber 1 to permit the removal of dirt and sediment in the usual way.

Fuel is conducted from' the fuel bowl directly to the emulsifying` chamber 4, hereinbefore vreferred to. The chamber 4 is formed within a sleeve 25 rotatably mounted in a fixed sleeve :26, which is suitably supported in a recess formed in the main casting B and held against rotation by any desirable means. The upper end of the sleeve 25 is closed by a cap member 27, seated in a recess 28 forming a shoulder on the upper end,4

of said sleeve rv25 and held in engagement with the sleeve by means of the fuel inlet tube29, the lower end of which is threaded as indicated at 30, and screwed into a recess 31, formed in a portion 32 of the casting B, which projects downwardly from said casting into the fuel bowl and has a fuel passage 33 formed therein, which communicates with the recess 31. At its lower end the passage 33 is enlarged as indicated at 34 to receive a calibrated plug 35, having a fuel metering restriction 36 therein, and which is screwed into the enlargement. All of the fuel supplied to the mixture at all engine speeds passes through the metering plug 35.

The fuel inlet tube 29, nereinberore referred to, is provided with a passage 37, which registers ed to supply fuel for idling and additional high speed fuel outlets comprising a plurality of pairs of orifices 39. At low speeds with closed throttle,

the suction which is maintained within the chamber 4 is sufficient only to lift fuel to a point above the orifices 38, so that these orices onlyl supply fuel at such times, but as the throttle is opened and the engine speed increases, the suc- -tion in the chamber 4 is effective to lift fuel to l which are adapted to supply the primary emulsion theorices 39 which become effective successively as the engine speed and the suction effective 'on the fel tube increases'to supply additional fuel to the emulsifying chamber 4 at higherl engine speeds. j

The rotatable sleeve 25 is provided with two outlet orifices 40 and 41, as shown in Fig. 4, co-

operating respectively with passages 42 and 43,

or mixture of fuel and yair to the-main intake passage at points above and below the throttle, respectively. The passage 42 communicates with a groove or channel 44'formed in the outer surface of the Venturi tube 6, thereinbefore referred to, while the ,passage 43 communicates with another channel 45, formed in the vexterior surface of said Venturi tub. The channel 44 com.-

muncates with the interior of the Venturi tube `through aplurality of orifices 46, while the channel 45 communicates with the point of greatest suction or partial vacuum in said tube through a lplurality ofA narrow slots 47, as shown in Fig. 4,

" to said throttle valve.V

Airis supplied to-the emulsifying chamber 4 by means of a passage 50 formed in the casting B at one side ofthe sleeve 25 and vextending downwardly between the fixed sleeve 28 and the casting, in aidirectionsubstantially parallel to said sleeve 25. The intakeend'of this passage is controlled by a iiange 51 projecting laterally from the upper end of the sleeve 25 and adapted to open and close the passage 50 as the sleeve 25 is rotated by means of an arm 52 which projects laterally from the sleeve at a point above the float chamber and is provided with an orifice 53 in its outer. end to. which a suitable operating connection extending to a point convenient to the operator of the vehicle is adapted to b e connect/ed. The air admitted to the passage 50 enters the chamber 4 at the lower end thereof through a passage 54 surrounding the fuel inlet tube 29, as clearly shown in Fig. 4. As the sleeve 25 is rotated to bring the orifice 40 into registry with the passage 42, so as to supply fuel mixture above the throttle when the latter is closed, for. idling or very low speed operation, the flange 51 is moved toward position to close or partially close the passage 50 in order toprestrict the admission of air through said passage and providea mixture suiiiciently rich inv fuel content to properly opcrate Athe lengine. under such operating conditions. y

The orifices 40 and 41 are positioned in staggered relation to each other so that when the orifice 40 is fully in register with the passage 42, thel orifice 41 is in a position where the passage 43 is entirely closed. However, it is preferable that the orifices 40 and 41 be so positioned that 110 the orifice 40 begins to register with the passage '42. The orifices may be so positioned in the sleeve 25 that the opening of the passage 42 before -the passage 43 is entirely closed overlaps the opening of the passage 43 to whatever extent may be desired, to secure a mixture of the most nearly desirable proportions. Moreover, if desired, a sleeve 25 may be employed in which the orifices 40 and 41 are so positioned that when one of the above, mentioned passages 43 and 42 is opened, the other is entire-ly closed at all times. In the preferred form of the invention shown herein the passage 43 is partially opened before the passage' 42 is entirely closed, and when the throttle is in position where the suction effective on the ports 125 46 is greater than that effective on slots 47, and the passages 42 and 43 are both partially open, air may enter the fuel feedingv orifices 47 and, passingthrough the passage 43, may mix with the primary fuel mixture fiowing from the chamber 4 130 through the passage y42. Also when the throttle 9 is relatively wide open this action may be reversed. Because of the higher suction existing at the orifices 47, a flow of air may take place through ythe orifices 46, passages 44 and 42 into the cham- 135 ber 4, and thence through the passage 43 and orifices 47vinto the main mixing chamber when the passages 42 and 43 are partly open.

Carburetors of this general typeA are usually provided with a main air intake passage of fixed 140 area, or one which is provided with a mechanically operated choke valve, which is adapted to be fully closed to choke the carburetor to facilitate starting of the engine, or during normal running conditions is intended to be fully opened. 145 In a devicel of this character the suction at the jets and the fiow of air through the carburetor is determined by the position of the throttle and la restriction such as is usually providedadjacent f said jets, as for instance, a Venturi tube. Under i l aprecia certain voperating conditions, for example, when the load is increased while the throttle remains stationary, the velocity of flow through the intake. passageadjacent the jets and the suction effective thereon is reduced. This will result in a reduction in fuel flow, which is generally undesirable under such operating conditions. According to the present invention, means are provided to automatically regulate the admission of air to the carburetor in accordance with the suction therein, the admission of air being restricted when the suction tends to' reduce and increased when the suction tends to increase, whereby objectionable uctuations in the suction effective on the jets owing to change in load and other variations in operating conditions is avoided. Y

For this purpose the valve 3, hereinbefore referred to, is'provided. This valve is secured to a rock.- shaft 601V journalled in the main casting A and when the engine is not running, the valve occupies the position shown in Fig. 4; where it completely closes the main air inlet 61, which supplies air to the chamber 2, previously referred to. Integral with the valve and projecting therefrom into the chamber 2 are arms 62 pivotallly connected at their inner ends to short links 63, which are pivotally connected to the upper end of a piston rod 64 by means of a pin 63a, and a piston 65, secured to the lower end thereof, is slidable in a cylinder 66, formed in a depending portion of the casting A, said piston and cylinder constituting a dash pot for controlling the movements of the valve 3. The valve is normally urged toward closed position by a spring 67freceived between the piston and a cup-shaped member 63. secured to axrod 69, which extends through a plug 70, screwed into the lower end of the cylinder 66, and constituting a closure member there- The rod is provided with a handle 71 on that end which projects outside the plug and is threaded intermediate its ends, as indicated at 72.L This threaded portion of the rod engages the wall of the casting A to slide freely therein and permits fuel toA bei/drawn from the dash pot into the chambei 2fthrough the. space around the rod by the suction maintained inthe chamber 2. Inl

order to prevent accumulation of this fuel in the bottom of the chamber 2, a passage 75 is provided which communicates with the atmosphere, as shown in Fig. 1, permitting air to vbe drawn through the passage and around the rod 64 through the above mentioned space. Ihis air will atomize anyl fuel escaping from the dash pot cylinderaround said rod and will carrysuch fuel into the mixing chamber. Since fuel is drawn out of the dalsh pot cylinder in the manner above described, it is necessary. to provide means for keeping the said cylinder lled with fuel. For

this purpose an angular passage 76 is bored in the Awall of the main'casting A, as illustrated in Fig. 6

fof the drawings. This passage communicates with the .cylinder 77 of an accelerator pump, more 'fully described hereinafter, bymeans of anorifice vrL78 through which fuel is adapted to vbe forced from the cylinder 77 into passage 76 whenever the pump fis operated to`supply i'uel for` accel- The above-mentioned pump for supplying additional fuel to enrichy the mixture duringv the acceleration period comprises the cylinder 77, which communicates with the fuel chamber 1 by means of the passage 79 and a piston 80 slidable in said cylinder. The piston is secured in any desirable manner to the lower end of a piston rod 81, pivotally connected at its upper end by pin 82 to a link 83, which is pivotally connected -to an arm 84, secured in any desirable manner yto a shaft 85, on which the throttle 9 is xed.

This,shaft is adapted to be operated by means of an operating arm 86, secured thereto in any desirable way and adapted to be connected at its upper end toany suitable form of connection extending to some point convenientv to the operator. It will be obvious that opening and closing movements of the throttle will reciprocate the piston 80 through the medium of the above described connections and said piston is" provided with a check valve 87 surroundngthe rod 81 and adapted to fit on top of the piston in position to close orifice 88 therein. A counter-clockwise movement` of the arm Se', which takes place onclosing movements of the throttle, will move the piston 80 downwardly during which movement the check valve 87 will open and allow fuel to pass from the lower part of the cylinder 77 through the piston into the upper part of said cylinder. Any subsequent opening movement of the throttle will lift .the piston 80 and force fuel from the space above said piston through a calibrated fuel inlet tube '90, which connects the upper part of the cylinder 77 with the chamber 2, as indicated in Fig. 6. This additional fuel will be carried into the engine by the air passing through the chamber 2 to form the somewhat enrichedmixture which is necessary to properly operate the engine during the acceleration period. At the same time fuel will be forced through the passage V78, as previously described, to replenish the fuel in the air valve dash pot. An orifice 91 connects the upper part of the cylinder 77 with the oat chamber, admitting air to the cylinder and providing the suction in said cylinder end becoming sufficient to lift the fuel therein to the tube 90.

The, normal closed or idling position of the throttle is determined by means of a stop member 95, secured on the end of the throttle shaft in any desirable way. An arm 96 projecting from said stop member supports a stop screw 97, which is threaded in said arm and is adjustable therein. This screw' is adapted to engage a fixed stop 98 projecting from the casting B to limit the closing movement of the throttle and by adjusting the screw 97, the closed position ofsaid 'throttle may be determined as desired.- rIhe stop member also has projecting therefrom v the arm 99, which is adapted to engage the stop member 98 to limit the opening movement of `said throttle.

It has been found desirable in order to secure the most satisfactory operation of an internal combustion engine to provide a mixture somewhat richer in fuel content during operation of said engine at low speeds and at high speeds, than at' the intermediate speeds which constitute the Inormal driving range.' It is, therefore, desirable in order to secure the most satisfactory and economical operation possible, to provide means for supplying a relatively lean fuel mixture during` on intermediate throttle positions. This admlslos sion of air reduces the suction effective' on the outlet ports of the fuel tube 29, thereby reducing the amount of fuelilow therefrom and at the same time slightly increases the amount of air admitted to the primary mixture conduit.

The means for admitting air as described com- .prises a passage 100 formed in a rib 101, formed on the casting B as illustrated in Fig. 5. The passage 100 communicates with the channel 45 by means of an orice 102 and at its upper end connects with a passage 103 of substantially rectangular cross section, and controlled by a plate 106, which is secured to the throttle shaft 85 -and is adapted to admit air to the passage 103, as later set forth. This passage only communicates with the passage 100, a 4plug 103abeing providedto prevent communication between the passages 103 and the channel 44, which supplies mixture through the orifices46 to the intake passage, for idling and low speed operation. The plate 106 is provided with a slot 107, which, in certain positions of the throttle, is adapted to admit air to the passage ,103, while in other positions of said throttle, the plate entirely closes the passage 103. Wh en the throttle is substantially closed, or in the lidling\position, the plate 106 is` in the position shown in Fig. 5 with the plate 106 closing passage 103. Movement of the throttle towards its open position will bring the slot 107 into registry with the passage 103 to admit antiiereto, the slot being Afully in registry with the passage when the throttle is in some intermediate position approximating normal driving speed. On further opening movement of the throttle toward its fully open position, the slot 107 is gradually moved out p of registry with the passage 103 until said passage is again'closed at full open position of said throttle.

In addition to the above described/plate 106 for controlling the ow of air through the passages 100 and 103, as above described, an automatic valve is provided in the passage 103 which is suction operated and controls the flow through said passage. This valve is indicated at 108 in Fig.'7 and consists of a rectangular flap pivoted on a pin 109, secured in the casting B and extending across the passage 103, as` indicated in Fig. 5. This valve is normally heldin its closed position by means of a weight 110, secured to the valve adjacent its free edge, as shown in Fig. 7. When the plate 106 is in position to permit a flow through the passages 100 and 103, any increase of `suction within the mixing chamber will cause the `valve 108 to open to admit more air to flow through said passages. 1 L

While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be4 adopted, all comingwithin the scope of the claims ,which'follom What is claimed is as follows: A

l. A carburetor of the class describedwzomprising a primary mixing chamber, an air supply passage communicating therewith, a main intake passage adapted to communicate with the intake manifold and forming a secondary mixing chamber, a throttle valve in said intake passage for controlling the flow therethrough, a plurality of conduits connecting the primary mixing chamber with the secondary mixing chamber on opposite sides of the throttle, a valve movable within said mixing chamber to regulate the flow through said conduits, and a fuel supply tube projecting into said mixing chamber and provided with a plurality of fuel inlet ports. f

2. A carburetor of the class described comprising a primary mixing chamber, an air supply passage communicating therewith, a lmain intake passage adapted to communicate `with the intake manifold and forming a secondary mixing chamber, a throttle valve in said intake passage for controlling the flow therethrough, a plurality of conduits connecting the primary mixing chamber with the secondary mixing chamber on oppogsite -sides of the throttle, a valve movable within said mixing chamber to render said conduits alternately effective, and a fuel supply tube projecting into said mixing chamber and provided with a plurality of fuel inlet ports.

3. A carburetor of the class described comprising a primary mixing chamber, an air 'supply passage communicating therewith, a main intake passage adapted to communicate with the intake manifold and forming a secondary -mixing chamber, a throttle valve in said intake passage for controlling the iiow therethrough, a plurality of conduits connecting the primary mixing chamber with the secondary mixing chamber on opposite sides of the throttle, a valve movable within the said mixing chamber to render said conduits alternately effective, a fuel supply tube projecting into said mixing chamber and provided with a plurality of spaced inlet ports, and means operated by said valve for varying the suction within the mixing chamber whereby 'said inlet ports are rendered effective successively.

4. A carburetor of the class described corn-` prising a primary mixing chamber, an air supply passage communicating therewith, a main y intake passage adapted to communicate with the intake manifold and forming a secondary mixing chamber, a throttle valve in said intake passage for controlling the flow therethrough, a plurality of conduits connecting the primary mixing chamber with the secondary mixing chamber on opposite sides of the throttle, a valve movable within said mixing chamber to control the ow through said conduits, a. fuel supply tube projecting into said mixing chamber and provided with a plurality ofspaced inlet ports, means operated 'by said valve for variably restricting the air supply passage to control the mixing chamber suction whereby the inlet ports are rendered successively effective.

5. A carburetor of the class described comprising a substantially vertical main intake passage forming a secondary mixing chamber, a fuel reservoir, a cover plate therefor lying in a substantially horizontal plane, a primary mixing chamber. formed in said cover plate, fuel inletv means comprising a fuel tube depending from and integral with said cover plate and projecting into the fuel reservoir and a primary mixture conduit also formed in said cover plate and vfadapted to convey the primary mixture to said secondary mixing chamber. l 6. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means forsupplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, said dash pot having a piston secured to a rod, saidrod extending from the dash pot into saidY intake passage and being slidable ina bore formed in the wallof said intake passage and a passage connecting said bore with the atmosphere.

7. A carburetor ofthe class describedcomprising a fuel-4 reservoir; a main intake passage, means for supplying fuel thereto, an air inlet Leraars therefor, a suction operated air valve controlling 'said inlet, a liquid dash pot controlling movel to the dash pot on opening movements of the throttle.

8. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, means operated on opening movements of the throttle for enriching the mixture and means whereby said mixture enriching means is operative to supply fuel to the dash pot.

9. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, afpump operated by the throttle to supply additional fuel to the mam intake passage and means whereby said pump is effective to supply fuel to the dash pot.

10. A carburetor of the class described comprising a fuel reservoir, a main intake passage,

means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, an auxiliary fuel chamber adapted tosupply additional fuel to the mam intake passage during the acceleration pei'1od and a passage connecting said auxiliary fuel chamber with the dash pot to supply fuel thereto.

11. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid' dash pot controllingmovements of said valve, a fuel pump comprising a cylinder and a reciprocating piston therein, and a passage connecting the upper portion of said pump cylinder with the dash pot to supply fuel thereto.

12. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, an auxiliary fuel chamber adapted to be filled with fuel on opening movements of the throttle to supply additional fuel to the main intake passage and a passage connecting the upper part of said chamber with the dash pot whereby the fuel is supplied to the dash pot on opening movements of the throttle.

13. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet,-a dash pot comprising a cylinder and for regulating the proportions of the fuel mixture comprising an auxiliary passage for supplying air to said intake passage, a throttle, means operated by said throttle for controlling said auxiliary passage, vsaid means being so constructed that the auxiliary passage is opened when the throttle is partially opened and is closed when the throttle is closed or fully opened.

15. A carburetor ofthe class described comprising a fuel reservoir, a main intake passage, conduits for supplying a primary mixture of fuel and air thereto, means for regulating the proportions of the fuel mixture comprising an auxiliary passage for supplying air to said conduits, a throttle, means operated by said throttle for controlling -said auxiliary passage, and an automatic valve for controlling said passage.

16. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying air thereto, a primary mixing chamber for supplying a primary mixture of fuel and air thereto, a throttle regulating the flow through the main intake passage, and means for controlling the proportions of said primary mixture comprising a passage admitting air to said primary mixing chamber, means operated by the throttle for controlling the ow through said last named passage, and a suction operated valve controlling said passage.

' 17. A carburetor of the class described comprising a fuel reservoir, a main intake passage, means for supplying fuel thereto, an air inlet therefor, a suction operated air valve controlling said inlet, a liquid dash pot controlling movements of said valve, said dash pot having a piston secured to a rod slidable in a bore in the 'wall of said intake passage, a passage connecting said bore with the atmosphere whereby air is admitted to said bore to atomize fuel passing therethrough and prevent accumulation in the intake passage of fuel passing through said bore and a drain passage connecting with said intake passage whereby any fuel Which accumulates therein is permitted to escape.

18. A carburetor for internal combustion engines comprising a fuel reservoir, a cover plate therefor, a recess formed in said cover plate, a primary mixing chamber positioned in said recess and spaced from the wall of said recess to provide means to admit air to said mixing-chamber,

with the fuel reservoir, and means conveying the v primary mixture from said primary mixing chamber to said secondary mixing chamber.

19. A carburetor for internal combustion engines comprising a fuel reservoir, a cover plate therefor, a recess formed in said cover plate, a primary mixing chamber positioned in said recess ,and spaced 'from the wall of said recess to ,pro-

vide means to admit air to said mixing chamber, a secondary mixing chamber also formed in said cover plate, said cover plate having a depending portion extending into the fuel in said reservoir and having a fuel supply conduit formed therein and connecting saidprimary mixing chamber with the fuel reservoir, and a. passage formed in said cover plate for conveying the primary mixture from the primary mixing chamber to the secondary mixing chamber. 

